Casting of aluminum silicate refractories



April 18, 1933. SCHROEDER" 1,903,944

CASTING OF ALUMINUM SILICATE REFRACTORIES FiledOct. 9, 1931 FIGJ.

a FIG. 3.

IN V5 N TOR FEEDER/C V. SCHROEDER BY Mo ATTORNEYS Patented Apr. 18, 1933 UNITED STATES PATENT OFFICE FREDERIC WILLIAM SCHROEDER, OF LOUISVILLE, KENTUCKY, ASSIGNOR TO CORI-IAR'I.

REFRACTORIES COMPANY, OF LOUISVILLE, KENTUCKY, A CORPORATION OF DELA- WARE CASTING OF ALUMINUM SILICA'IE' REFRACTORIES Application filed October 9, 1931. ScriaLNo. 567,950.

The manufacture of refractory blocks and pieces by casting melted aluminum silicates into desired shapes has for a number of years been an established industry and blocks made by such processes have been widely accepted by the trade, the blocks having been produced in molds made of sand bonded with linseed oil as is described in United States Patent No. 1,615,750.

Prior to this invention it has been difficult,

if not impossible, to cast pieces of such refractories having a central hole or having a recess in the face thereof, although there was a demand for such shapes. In attempting to make such castings with sand cores most, or if not all, of the blocks developed cracks on solidifying. From a study of defective blocks produced in this way I associated the defects in question with some thermal property and .I have discovered that such defects may be avoided and sound cored castings may be obtained by using as a core material particles or grains having high thermal conductivity and low thermal expansion, (high and low being here used as meaning substantially higher and lower than the similar properties of sand) such for instance as a material simi- .lar to the aluminum silicate being cast and preferably identical therewith.

Referring to the accompanying drawing. in which corresponding parts are designated by corresponding marks of reference Figure 1 is a perspective view of one form of a cast refractory easily produced by the use of this invention, but which had not prior thereto been successfully cast;

Figure 2 is a sectional, view of the mold in which the block of Figure 1 may be cast and embodying this invention.

The mold shown in Figure 2 is in contour of the standard type used for many years in the attempt to cast trough blocks of the shape shown in Figure 1. It consists of slabs a toform the six sides of the block and core slabs b resting on the bottom slab a to form a raised portion thereon to mold the trough c of the block. As before stated it has heretofore been the practice to form all these slabs from sand bonded with linseed o l. With such a construction cracks indicated by the dotted lines (Z in Figure 1 developed on the cooling of the block.

I have discovered that if the core slabs b be molded from grains produced by crushing pieces of the aluminum silicate refractory which is to be molded, suitably bonded, as by oil, the cracks do not appear.

From a consideration of the conditions attending on the molding of such blocks 1 believe the desirable result to be due to the relatively low thermal expansion and/or the relatively high heat conductivityof the aluminum silicate slabs as compared to the sand slabs. This belief arises from the following consideration. The material to be molded consists essentially of alumina. and silica, the alumina percentage being higher than that of silica and is cast at a tempera ture of approximately 1800 C. A thin skin of solidified material (mullite bonded with 7 glass) forms within a few seconds, the skin on formation probably having a temperature of about 1500". Heat from the block passes through this skin to the core slabs so that as the block is contracted on coolingthe core is expanding on heating. Due to the relatively low conductivity of the slabs made of sand the heating of such a slab is slow so that its maximum temperature and expansion occurs after the block has substantially solidso ified and become rigid. Therefore we have a contracting block and a rapidly expanding core with the result of creating compression on the core and tensile strains in the block, tending to split the latter. As the thermal expansion of a cast material is much less than that of silica the use of slabs of grains of the cast material tends to reduce this strain and as the heat conductivity of the cast material is much higher than that ofsan d the core reaches its maximum temperature and hence volume much earlier and while the block is still plastic and still capable of yielding without rupture.

In'lieu of grains formed from pieces of the cast aluminum silicate I may use grains of other aluminum silicates or grains of crystalline aluminum oxide, either synthetic or natural, provided the heat conductivity of such material is high and its thermal expansion is low as compared with that of quartz.

Having thus described my invention what I claim is 1. A core for molding cast aluminum silicates formed of grains of aluminum silicate and a suitable bond.

2. A core for molding cast aluminum silicates formed of grains having low thermal expansion and high heat conductivity as compared to sand.

3. A core for molding cast aluminum silicates formed of grains of crystalline aluminum oxide and a suitable bond.

In testimony whereof I hereunto aflix my signature.

FREDERIC WILLlAM SCHROEDER. 

